Trimming of local oscillation in an integrated circuit radio

Abstract

A method and apparatus for trimming of a local oscillation within a radio frequency integrated circuit (RFIC) includes processing that begins when an RFIC receives a radio frequency (RF) signal having a known frequency. The processing then continues when the RFIC mixes the RF signal with a receiver local oscillation to produce a low intermediate frequency (IF) signal, which may have a carrier frequency of zero (i.e., a baseband signal) or up to a few mega Hertz). The processing then continues when the RFIC demodulates the low IF signal to produce demodulated data. The processing then continues as the RFIC determines a DC offset from the demodulated data, where the DC offset is reflective of the difference between the known frequency and the frequency of the receiver local oscillation. The processing then continues as the RFIC adjusts the receiver local oscillation to reduce the DC offset when the DC offset compares unfavorably with an allowable offset threshold.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of and claims priority to U.S. patent application having an application Ser. No. 10 / 243,861 and a filing date of Sep. 13, 2002, which application is a continuation-in-part of U.S. patent application having an application Ser. No. 10 / 134,797 and a filing date of Apr. 29, 2002; and in which both applications are incorporated herein by reference in this application.BACKGROUND OF THE INVENTION [0002] 1. Technical Field of the Invention [0003] This invention relates generally to wireless communication systems and more particularly to frequency modulated (FM) radio receivers used in such systems. [0004] 2. Description of Related Art [0005] Communication systems are known to support wireless and wire lined communications between wireless and / or wire lined communication devices. Such communication systems range from national and / or international cellular telephone systems to the Internet to point-to-point in-h...

AI Technical Summary

Benefits of technology

[0011] The method and apparatus for trimming of a local oscillation within a radio frequency integrated circuit (RFIC) as disclosed herein substantially meet these needs and others. One embodiment of such a method and apparatus includes processing that begins when an RFIC receives a radio frequency (RF) signal having a known frequency. The processing then continues when the RFIC mixes the RF signal with a receiver local oscillation to produce a low intermediate frequency (IF) signal, which may be a signal having a carrier frequency of a zero hertz to a few megahertz. As part of the mixing, the RFIC sets it receiver local oscillation to a frequency that is intended to match the known frequency. However, due to process variations in the fabrication of the RFIC and component tolerances, the frequency of the receiver local oscillation will most likely not exactly match the known frequency. The processing then continues when the RFIC demodulates the low IF signal to produce demodulated data. The processing then continues as the RFIC determines a DC offset from the demodulated data, where the DC offset is reflective of the difference between the known frequency and the frequency of the receiver local oscillation. The processing then continues as the RFIC adjusts the receiver local oscillation to reduce the DC offset when the DC offset compares unfavorably with an allowable offset threshold. In other words, the receiver local oscillation is adjusted such that its frequency more closely matches the known frequency, thereby reducing the DC offset and the adverse affects caused thereby.

[0012] Another embodiment of such a method and apparatus of the present invention include its use in a fractional-N frequency synthesizer generating the local oscillation using a crystal reference. Specifically, during test of a radio frequency integrated circuit (RFIC), the local oscillation module receives a crystal offset fractional value and generates a fractional-N divider value of the local oscillation based on the crystal offset fractional value, an integer value, and a set fractional value. During operation of the RFIC, the local oscillation module receives an operational offset fractional value and generates the fractional-N divider value based on the crystal offset fractional value, the integer value, the set fractional value, and the operational offset fractional value. As such, by adjusting the local oscillation to more closely match the RF frequency of received RF signals, frequency offset is reduced, as well as the adverse affects caused thereby.

Problems solved by technology

However, due to process variations in the fabrication of the RFIC and component tolerances, the frequency of the receiver local oscillation will most likely not exactly match the known frequency.

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